The invention relates to compression springs, especially elastomeric compression springs or cushion pads which are used in off-the-road vehicles, or in the draft gears of railroad cars. More particularly, the invention relates to cusion pads which are composed of polyester elastomeric materials developed and manufactured by Du Pont Company and sold under the company trademark HYTREL which, as indicated in U.S. Pat. No. 4,198,073 at lines 19-25 of column 1, is made from three ingredients, namely, (1) dimethyl terephthalate, (2) polyglycols such as polytetramethylene ether glycol, polyethylene ether glycol, or polypropylene ether glycol, and (3) short chain diols like butanediol and ethylene glycol.
U.S. Pat. No. 4,198,037 discloses a cushion pad which is made of such material by, first, individually molding a cylindrical pad, then annealing the pad, and finally compressing the annealed pad to remove any set the pad might develop upon compression. As indicated, the compression pads are individually molded because they are too large to be formed by the extrusion process. Further, a weight is used to press, by gravity, upon a pad as it is molded.
It has been found that, contrary to the teaching of this patent, compression pads of HYTREL polyester elastomeric material can be produced in an elongated, cylindrical slug of material, cut into a plurality of pads which are then individually compressed to form finished pads without going through the expensive and time consuming process of annealing the pads.
Briefly stated, the invention is in a method of forming a compression spring or cushion pad which is composed of a Hytrel polyester elastomer by (I) heating solid material of the elastomer to a molten mass, (II) charging the molten mass to a heated cylindrical chamber, (III) cooling and solidifying the mass in the chamber under pressure which is at least 1000 pounds per square inch (psi), (IV) removing the solidified cylinder from the chamber and cutting it crosswise into a plurality of pads, and (V) momentarily compressing the cut pads axially to remove any adverse set which develops upon initial compression of an uncompressed pad.
Thus, the invention has a two fold advantage over the prior art. It eliminates the annealing process and the expense of having to stock the many molds which are required to individually mold each pad.